The present invention relates to an industrial vehicle
such as a forklift truck.

The forklift truck is widely used as the industrial vehicle
to perform loading operation (operation for picking up or putting down load) in
a factory yard. In such a forklift truck, an operator or driver of the forklift
truck is engaged in not only driving the vehicle but also loading. The driver therefore
frequently leaves the seat of the vehicle in an idling state, which may cause a
dangerous state. To avoid it, the generic Japanese Unexamined Utility Model Publication No. 2-51934 (US 5 109 945) proposes a safety device for use in restoring a running state of the
vehicle after the driver leaves the seat.

In the above reference, the seat is provided with a seat
switch for detecting whether the driver is seated. If the seat switch detects that
the driver is not seated, energization of a solenoid valve is broken. The solenoid
valve changes flow of hydraulic fluid into a transmission (clutch mechanism) connected
to an engine. If the driver who has left the seat returns to the vehicle, when the
driver is seated and a manipulation position of a lever for forward or backward
movement is a neutral position, the solenoid valve is reenergized.

Meanwhile, there is a way that a detection switch directly
detects whether the manipulation position of the lever is a position of the forward
movement or a position of the backward movement and judges that the neutral position
is detected if the manipulation position is neither the position of the forward
movement nor the position of the backward movement. In the forklift truck using
such a detection way of the manipulation position, if the solenoid valve is reenergized
under the condition of the return of the safety device as described in the above
reference, the forklift truck has the following problems.

That is, in the case of the above detection way, if the
connection between the detection switch and a controller is broken, the controller
erroneously judges that the manipulation position of the lever is the neutral position.
Therefore, if the driver leaves the seat with the lever manipulated in the position
of the forward or backward movement and the connection between the detection switch
and the controller is then broken in this state, when the driver is seated, it is
erroneously judged or detected that the manipulation position of the lever is the
neutral position, thereby to restore the running state. Consequently, the running
state is restored only by the judgment of the seat switch that the driver is seated.
Therefore, when the safety device of the above reference is applied to the forklift
truck which uses the above detection way, the safety device is subject to an influence
(such as disconnection) of various detection switches for detecting condition that
restores the running state, so that reliability of the safety device deteriorates.
If the running state of the vehicle, especially with the torque converter is restored
under the above condition, the vehicle may run away due to a creep phenomenon of
the toque converter by reenergizing the solenoid valve.

The present invention is directed to an industrial vehicle
which prevents erroneous return of the running state due to erroneous detection
of various detection switches by adding driving manipulation of the driver to the
condition of the return of the running state when the running state is restored
after the driver leaves the seat, thereby to improve reliability of the return of
the running state.

SUMMARY OF THE INVENTION

An industrial vehicle according to the present invention
provides the following features. The industrial vehicle has drive wheels driven
by an engine. The industrial vehicle includes a power transmission device, a driver
detection switch, a direction indication member, a position detection switch, an
electromagnetic control valve and a controller. The engine is connected to the drive
wheels through the power transmission device for transmitting output of the engine
to the drive wheels thereby to run the vehicle. The driver detection switch detects
whether a driver of the vehicle is seated in a driver's cabin in a driving position.
The direction indication member is manipulated by the driver for indicating forward
or backward movement of the vehicle. The position detection switch detects a manipulation
position of the direction indication member. The electromagnetic control valve changes
flow of hydraulic fluid supplied into the power transmission device. The controller
controls an energizing state of the electromagnetic control valve. The controller
is electrically connected to the driver detection switch and the position detection
switch. The controller breaks energization of the electromagnetic control valve
if the driver detection switch detects that the driver is not seated. The controller
energizes or reenergizes the electromagnetic control valve if the driver detection
switch detects that the driver is seated and the position detection switch detects
that the manipulation position of the direction indication member is a neutral position
and then a forward or backward position.

Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with the accompanying
drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed
to be novel are set forth with particularity in the appended claims. The invention
together with objects and advantages thereof, may best be understood by reference
to the following description of the presently preferred embodiments together with
the accompanying drawings in which:

FIG. 1 is a side view showing a forklift truck according to a preferred embodiment
of the present invention;

FIG. 2 is a block diagram showing a controlling structure of the forklift truck;

FIG. 3A is a timing chart showing an input-output signal of a controller of
the forklift truck;

FIG. 3B is a timing chart showing an input-output signal of the controller of
the forklift truck; and

FIG. 4 is a circuit diagram showing a connecting state of a relay of the forklift
truck.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a preferred embodiment of the
invention. In the present embodiment, the invention is embodied to a counterbalanced
forklift truck with reference to FIGS. 1, 2, 3A, 3B and 4. In the following description,
"forward" and "backward" directions are based on the state where a driver of the
forklift truck faces forward (in a direction of forward movement) of the forklift
truck.

As shown in FIG. 1, a forklift truck 10 that serves as
an industrial vehicle includes a body 11 of the vehicle and a loading apparatus
14 provided forward of the body 11. The loading apparatus 14 has a mast 12 and a
fork 13. A driver's cab 15 is provided in the middle of the body 11. Drive wheels
(front wheels) 16 are provided in the lower part of the body 11 forward of the body
11 and steered wheels 17 are provided in the lower part of the body 11 backward
of the body 11. An engine 18 is mounted on the body 11 and is connected to the drive
wheels 16 through a transmission 19 that serves as a power transmission device.
The forklift truck 10 of the present embodiment is an engine type forklift truck
where the drive wheels 16 are driven by the engine 18 to run the forklift truck.

The transmission 19 includes a torque converter 20, a clutch
mechanism 21 for forward movement and a clutch mechanism 22 for backward movement
to form an automatic transmission. Each of the clutch mechanisms 21 and 22 is a
hydraulic type clutch mechanism. Hydraulic fluid is supplied to the clutch mechanisms
21 and 22 through a solenoid valve for forward movement 23 (shown in FIGS. 2 and
4) and a solenoid valve for backward movement 24 (shown in FIGS. 2 and 4) each of
which serve as an electromagnetic valve. That is, the flow of the hydraulic fluid
into the transmission 19 is changed under the control of the solenoid valves 23
and 24. When the solenoid valve 23 is energized, the hydraulic fluid is supplied
to the clutch mechanism 21 to run the forklift truck 10 forward. When the solenoid
valve 24 is energized, the hydraulic fluid is supplied to the clutch mechanism 22
to run the forklift truck 10 backward.

The driver's cab 15 has a seat 25 on which the driver is
seated. In the forklift truck 10 of the present embodiment, when the driver is seated
in the seat 25, it is regarded that the driver is seated in the driver's cab 15
in a driving position. When the driver is seated in the driver's cab 15, the driver
is in a seating state. When the driver is not seated in the driver's cab 15, the
driver is in a non-seating state. The seat 25 is provided with a switch 26 for detecting
whetherthe driver is seated, which serves as a driver detection switch. The switch
26 detects whetherthe driver is seated in the driver's cab 15 in a driving position
and outputs the detection result as a detection signal. The detection signal of
the switch 26 is hereinafter referred to as "seating signal".

In the driver's cab 15, a steering column 27 is provided
forward of the seat 25. A steering wheel 28 is mounted on the steering column 27
to change a steering angle of the steered wheels 17.

A lever (shift lever) 29 for forward or backward movement
is provided on the steering column 27 and serves as a direction indication member
for indicating a running direction of the vehicle. In the present embodiment, the
lever 29 is capable of selectively indicating "forward movement" or "backward movement"
as a running direction of the vehicle. In the present embodiment, when the lever
29 is manipulated so as to be inclined from a neutral position forward, the lever
29 selectively indicates "forward movement". When the lever 29 is manipulated so
as to be inclined from the neutral position backward, the lever 29 selectively indicates
"backward movement". The manipulation position in which the lever 29 selectively
indicates "forward movement" is a forward position and the manipulation position
in which the lever 29 selectively indicates "backward movement" is a backward position.

The steering column 27 is provided with a switch (direction
switch) 30 for detecting forward or reverse movement (shown in FIGS. 2 and 4), which
detects the manipulation position (the forward or backward position) of the lever
29. The switch 30 serves as a position detection switch. The switch 30 outputs the
respective detection signals in accordance with the manipulation positions of the
lever 29. It is noted that the switch 30 does not output the detection signal when
the lever 29 is in the neutral position (or the detection of the neutral position
is not performed). When the switch 30 detects the forward position as the manipulation
position of the lever 29, the detection signal is hereinafter referred to as "forward
signal". When the switch 30 detects the backward position as the manipulation position
of the lever 29, the detection signal is hereinafter referred to as "backward signal".

An accelerator pedal (vehicle acceleration member) 31 is
provided on the lower part of the driver's cab 15. The accelerator pedal 31 indicates
acceleration (running) of the forklift truck 10 and adjusts its running speed.

The body 11 is provided with a controller 32 which performs
various control of the forklift truck 10, such as running control. As shown in FIGS.
2 and 4, the switch 26, the switch 30 and a key switch 33 are electrically connected
to the controller 32. The key switch 33 detects manipulation position of a starting
switch key which starts or stops the engine 18, to output the detection result as
a detection signal. The detection signal of the key switch 33 is hereinafter referred
to as "key signal". The solenoid valve 23 is electrically connected to the controller
32 through a relay 34 for forward movement and the solenoid valve 24 is electrically
connected to the controller 32 through a relay 35 for backward movement.

The relay 34 has a normally closed contact ("b" contact)
34a for forward movement and a relay coil (electromagnet) 34b for forward movement.
When the relay coil 34b is deenergized to close the normally closed contact 34a,
the solenoid valve 23 is energized. The relay 35 has a normally closed contact ("b"
contact) 35a for backward movement and a relay coil (electromagnet) 35b for backward
movement. When the relay coil 35b is deenergized to close the normally closed contact
35a, the solenoid valve 24 is energized.

The following will describe running control executed by
the controller 32 and in particular control of an energizing state (energization
or break of energization) of the solenoid valves 23 and 24 with reference to FIGS.
3A, 3B and 4 in detail. The controller 32 executes the following control in accordance
with a previously stored control program. Both of FIGS. 3A and 3B are timing charts
showing input-output signals of the controller 32, respectively, and FIG. 4 is a
circuit diagram showing a connecting state of the relay.

When the driver is seated on the seat 25 of the driver's
cab 15 in the driving position and manipulates the starting switch key to start
the engine 18, the key signal of the key switch 33 and the seating signal of the
switch 26 are turned ON to input those signals into the controller 32. When the
engine 18 is started, electric power is supplied to the controller 32, the relays
34 and 35. Therefore, when the relay coils 34b and 35b are energized to open the
normally closed contacts 34a and 35a, the solenoid valves 23 and 24 are not energized.

When the driver manipulates the lever 29 from the neutral
position to the forward position after starting the engine 18, the forward signal
of the switch 30 is turned ON to input the signal into the controller 32. At this
time, the controller 32 turns an energizing signal ON to energize the solenoid valve
23 thereby to input the signal into the relay 34 as shown in FIG. 3A. Consequently,
when the relay coil 34b is deenergized to close the normally closed contact 34a,
the solenoid valve 23 is energized. When the driver pushes the accelerator pedal
31, the forklift truck 10 moves forward at the speed in accordance with the pushing
degree.

On the other hand, when the driver manipulates the lever
29 from the neutral position to the backward position after starting the engine
18, the backward signal of the switch 30 is turned ON to input the signal into the
controller 32. At this time, the controller 32 turns the energizing signal ON to
energize the solenoid valve 23 thereby to input the signal into the relay 35 as
shown in FIG. 3B. Consequently, when the relay coil 35b is deenergized to close
the normally closed contact 35a, the solenoid valve 24 is energized. When the driver
pushes the accelerator pedal 31, the forklift truck 10 moves backward at the speed
in accordance with the pushing degree.

Then, when the driver stops the forklift truck 10 and leaves
the seat 25 to turn the seating signal of the switch 26 OFF, the controller 32 turns
the energizing signal OFF in a predetermined delay time T of about 2 seconds. Therefore,
in the case where the solenoid valve 23 is energized, when the relay coil 34b is
energized to open the normally closed contact 34a, energization of the solenoid
valve 23 is broken as shown in FIG. 3A. On the other hand, in the case where the
solenoid valve 24 is energized, when the relay coil 35b is energized to open the
normally closed contact 35a, energization of the solenoid valve 24 is broken as
shown in FIG. 3B. That is, in the forklift truck 10 of the present embodiment, when
the driver leaves the seat 25, energization of the solenoid valves 23 and 24 is
broken regardless of the manipulation position ("forward position", "backward position"
or "neutral position") of the lever 29.

Then, when the driver is reseated on the seat 25, the seating
signal of the switch 26 is turned ON thereby to input the signal into the controller
32. When the seating signal is turned ON, if the forward or backward signal of the
switch 30 is turned ON, the controller 32 does not turn the energizing signal ON.
That is, when the seating signal is turned ON, the controller 32 judges whetherthe
manipulation position of the lever 29 is the neutral position. When each of the
forward and backward signals of the switch 30 is turned OFF, the controller 32 judges
that the manipulation position of the lever 29 is the neutral position.

At this time, the controller 32 detects that the manipulation
position of the lever 29 is the neutral position. Then, when any of the forward
and backward signals of the switch 30 is turned ON, the controller 32 turns the
energizing signal ON to reenergize the solenoid valve 23 or 24. When the forward
signal is turned ON, the controller 32 turns the energizing signal of the relay
34 ON to energize the solenoid valve 23. When the backward signal is turned ON,
the controller 32 turns the energizing signal of the relay 35 ON to energize the
solenoid valve 24.

In the forklift truck 10 of the present embodiment, when
the engine is started (or when power source is input), if the driver leaves the
seat once and then is reseated, a first condition of the return of a running state
is that the driver is seated and the manipulation position of the lever 29 is the
neutral position. Also, a second condition of the return of the running state is
that the first condition is formed and then the driver manipulates the lever 29
to the forward position or the backward position. If the first condition is formed
and then the second condition is formed, the solenoid valve 23 or 24 is energized
to restore the running state. That is, when the driver who has left the seat is
reseated in the driving position (or when another driver is seated in the driving
position), if he or she expresses intention of manipulating the lever 29 from the
neutral position to the forward or backward position, the running state is restored.
By so constructing the forklift truck 10 which is a vehicle with the torque converter
(automatic), even if the driver leaves the seat once with the lever 29 manipulated
to the forward or backward position and then is reseated, the vehicle does not run
away due to a creep phenomenon of the torque converter peculiar to this type of
vehicle. That is, when the driver leaves the seat once with the lever 29 manipulated
to the forward or backward position, if the lever 29 is returned to the neutral
position once and then manipulated to the forward or backward position, the running
state is restored.

Therefore, the present embodiment has the following advantageous
effects.

(1) When the driver leaves the seat so that the switch 26 detects non-seating
of the driver, the controller 32 breaks the energization of the solenoid valve 23
or 24. After the controller 32 detects that the driver is seated and that the manipulation
position of the lever 29 is the neutral position, if the manipulation position of
the lever 29 is located in the forward or backward position, the controller 32 energizes
the solenoid valve 23 or 24 to restore the running state. Therefore, when the driver
leaves the seat, energization of the solenoid valves 23 and 24 is broken regardless
of the manipulation position of the lever 29. On the other hand, when the driver
who has left the seat is reseated, the solenoid valve 23 or 24 is not reenergized
unless the driver expresses the intention of manipulating the lever 29 to the forward
or backward position. Consequently, erroneous running return due to erroneous detection
of various detection switches is prevented thereby to improve reliability of the
return of the running return.

(2) The condition of the return of the running state is that the driver manipulates
the lever 29 from the neutral position to the forward or backward position in addition
to the condition that the driver is seated and the lever 29 is in the neutral position.
Therefore, even the forklift truck 10 with the torque converter 20 (automatic) can
prevent it from running away against the driver's intention due to the creep phenomenon
in restoring the running state. Thus, the reliability of the return of the running
return is further improved. In addition, safety of the forklift truck 10 is further
improved.

(3) The seat 25 is provided with the switch 26, which detects whetherthe driver
is seated in the driver's cab 15 in the driving position. Since it is directly detected
by the switch 26 whether or not the driver is seated in the driver's cab 15 in the
driving position, the reliability of the return of the running return is improved.

(4) The condition of the return of the running state is formed by the driving
manipulation (indication of forward or backward movement) of the lever 29 by the
driver. Therefore, when the running state is restored, the driver does not need
special manipulation, so that the maneuverability of the forklift truck 10 is not
spoiled. In addition, the manipulation of the lever 29 is one of ways of reflecting
the driver's driving intention the most remarkably, which provides a safety device
that the driver's intention is reflected. That is, the running state can be restored
in accordance with the driver's intention.

The above embodiment may be modified as follows.

In the above embodiment, the seat 25 (the driver's cab
15) may be provided with a seat belt instead of the switch 26 to detect a wearing
state of the seat belt, so that energization or break of energization of the solenoid
valves 23 and 24 may be controlled. In this structure, if the seat belt is not worn,
the solenoid valves 23 and 24 are not energized, which obliges the driver to wear
the seat belt. Therefore, further safe running is achieved.

The above embodiment may be applied to the forklift truck
with a standing ride type driver's cab. In this case, the driver may operate a detection
switch provided in the driver's cab, such as floor switch so that the switch detects
whether the driver is seated in the driver' cab in the driving position from the
operation state of the switch. In this case, the driving position is a standing
position and the driver is seated in the driver's cab in the standing position.

The above embodiment may dispense with the relays 34 and
35 so that the controller 32 controls the solenoid valves 23 and 24 directly.

In the above embodiment, the structure of the solenoid
valves 23 and 24 may be modified. For example, 3-position 4-port valve may be used
instead of the solenoid valves 23 and 24 to switch the flow of the hydraulic fluid.

In the above embodiment, a switch type direction indication
member may be used instead of the lever 29 so that forward or backward movement
is indicated by manipulation of the switch.

In the above embodiment, the normally closed contacts 34a
and 35a of the relays 34 and 35 may be replaced by normally open contacts.

Although the above embodiment is embodied to the forklift
truck 10 that serves as an industrial vehicle, it may be embodied to the industrial
vehicle other than the forklift truck, such as towing tractor.

Therefore, the present examples and embodiments are to
be considered as illustrative and not restrictive, and the invention is not to be
limited to the details given herein but may be modified within the scope of the
appended claims.

An industrial vehicle (10) having drive wheels (16) driven by an engine
(18) the industrial vehicle including a power transmission device (19), a driver
detection switch (26), a direction indication member (29), a position detection
switch (30), an electromagnetic control valve (23, 24) land a controller (32), the
engine (18) being connected to the drive wheels (19) through the power transmission
device (19) for transmitting output of the engine (18) to the drive wheels (16)
thereby to run the vehicle, the driver detection switch (26) detecting whether a
driver of the vehicle is seated in a driver's cabin (15) in a driving position,
the direction indication member (29) being manipulated by the driver for indicating
forward or backward movement of the vehicle, the position detection switch (30)
detecting a manipulation position of the direction indication member, the electromagnetic
control valve (23, 24) changing flow of hydraulic fluid supplied into the power
transmission device, the controller (32) controlling an energizing state of the
electromagnetic control valve (23, 24) the controller (30) being electrically connected
to the driver detection switch (26) and the position detection switch (30),
characterized in that the controller (32) breaks energization of the electromagnetic
control valve (23, 24) if the driver detection switch (26) detects that the driver
is not seated, and in that the controller (32) energizes or reenergizes the
electromagnetic control valve (23, 24) if the driver detection switch detects (26)
that the driver is seated and the position detection switch (30) detects that the
manipulation position of the direction indication member (29) is a neutral position
and then a forward or backward position. The industrial vehicle according to claim 1, wherein the controller
(32), is electrically connected to the electromagnetic control valve (23, 24) through
a relay (34).The industrial vehicle according to claim 2, wherein the relay (34)
has a normally closed contact (34a) and a relay coil (34b).The industrial vehicle according to any one of claims 1 through 3, wherein
the power transmission device (19) is an automatic transmission with a torque converter
(20).The industrial vehicle according to any one of claims 1 through 4, wherein
the driver detection switch (26) is a switch for detecting whether the driver is
seated in a seat (25) provided in the driver's cabin.The industrial vehicle according to any one of claims 1 through 5, wherein
the direction indication member (29) is a shift lever.The industrial vehicle according to any one of claims 1 through 6, wherein
the position detection switch (30) is a direction switch.The industrial vehicle according to any one of claims 1 through 7, wherein
the electromagnetic control valve (23, 24) is a solenoid valve.